In most commercial and residential buildings air ducts pass either outside the building or in non-insulated areas of the building. Thus, the ducts present a problem of allowing drafts to pass from the ducts when air is not being passed from the ducts.
A number of U.S. patents have addressed this problem.
In U.S. Pat. No. 1,309,430 by W. J. Woodall a deflector plate is hinged to direct air flow. However, the deflector requires manual positioning and does not cut off potential cold drafts.
Similarly, in U.S. Pat. No. 2,284,912 by J. E. Maynard, et al, a damper is disclosed. As in other patents, however, the position of the damper is set and changed manually.
The advantage of the disclosed device lies in its ability to react without manual direction. Thus, forced air opens the duct air flaps which close due to their own weight when the forced air ceases.